Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$226.32	12.852%	$255.4066	$255.41	$255.40	$255.40
Purchase #2	$222.43	13.803%	$253.132	$253.13	$253.15	$253.10
Purchase #3	$81.89	5.634%	$86.5037	$86.50	$86.50	$86.50
Purchase #4	$196.36	5.350%	$206.8653	$206.87	$206.85	$206.90
Purchase #5	$229.83	11.155%	$255.4675	$255.47	$255.45	$255.50
Purchase #6	$208.85	8.457%	$226.5124	$226.51	$226.50	$226.50
Purchase #7	$116.65	4.803%	$122.2527	$122.25	$122.25	$122.30
7 purchase totals =	$1,282.33		$1,406.1402	$1,406.14	$1,406.10	$1,406.20